The present invention generally relates to towcables and more particularly to a system for distributing a tensile load within a towcable system.
Existing faired towcables utilize a single strength member so positioned within the fairing that the center of tension is sufficiently forward of the center of pressure and center of mass as to insure hydro-mechanical stability. In some cases the strength member comprises a cable of circular cross-section about which the fairing rotates. In other cases the strength member is molded so that its cross-sectional shape forms the fore portion of the fairing. An attached non-strength member tail section completes the towcable. Of course in the latter case the strength member rotates with the towcable.
A circular strength member is not compatible with a low-drag fairing cross-sectional shape because the nose section of a low-drag fairing is too narrow for the installation of an adequate size strength member. The usual practice is to use a non-optimum fairing where a portion of the fairing sides are straight and parallel and where the fairing pivots about a forward mounted circular strength member. The fairing's leading edge is usually determined by a U-shaped piece which surrounds the circular strength member and is fastened to the remaining portion of the fairing. Thus the use of a circular strength member results in both a low percentage of the fairing being occupied by a strength member and a poor drag coefficient.
A molded strength member can constitute the fore section of a low-drag fairing but any attempt to achieve a high packing density results in an undesirably high thickness to width ratio. A high thickness to width ratio can significantly increase the following negative factors. There is difficulty in keeping the center of tension sufficiently far forward even in a straight cable. The center of tension moves aft when the leading edge of a towcable is bent about a lateral axis. When similarly bent the highest tensional stress occurs in the portion of the strength member furthest from the bending center. The stress in this aft edge of the strength member is porportional to the fourth power of the strength member's thickness. In addition when similarly bent the strength member and thus the complete fairing tends to buckle laterally and assume an angle of attack with respect to the relative waterflow.
Some existing faired towcables, particulary the older towcables, devote a considerable portion of their internal space to electrical cables. This situation existed primarily because the signal from or to each transducer or hydrophone element would have its own circuit hard wired in a multiconductor cable. However, data telemetry systems involving frequency multiplexing and coaxial cables exist which can and do provide very large bandwidth channels in relatively small cables. Since the power and data channels are usually not in use simultaneously, properly designed electrical cables and switching and conversion techniques can make one cable serve for both power and data transmission. Thus, if modern power and data transmission techniques are employed space requirements for electrical cables can be minimized.